The overall objective of this project is to elucidate mechanisms controlling growth rates during catch-up (compensatory) and proportionate growth. Hypotheses to be tested are: a. catch-up growth and proportionate growth controls operate via mechanisms that depend on functions in addition to or other than classical or well-known endocrine functions, b. catch-up growth is limited in some cases by damage to peripheral growth mechanisms, c. the proportionate growth control has precedence over controls of growth in individual dimensions, d. energy wasting modifies the catch-up growth response, and e. the cortisone analogues have different potentials for producing short term and long term disturbance. Cortisone acetate and betamethasone acetate will be administered to rats during pregnancy or directly to the fetus and to the neonate. The following will be evaluated at the end of treatment, and at intervals during recovery: physical growth; skeletal maturation by X-ray or by staining of the skeleton after clearing in toto; cartilage ultrastructure and histochemistry by light and electron microscopy; synthesis of sulfated polysaccharides in vivo and in vitro, and synthesis of RNA, DNA, protein and collagen in vitro; organ weights; cell size and number of selected organs; and food efficiency for growth and maintenance of body weight.